The present invention relates generally to methods and apparatus for assembling integrated circuit components to substrates; and more specifically relates to improved methods and apparatus for singulating semiconductor devices after mounting to a substrate. Along with uses with other types of semiconductor devices, the present invention provides particular advantages with respect to the assembly of components including solar cells, such as in the forming of solar arrays.
The present invention will be described herein in the context of semiconductor devices. Semiconductor devices are typically formed using a semiconductor material wafer, such as a monocrystalline silicon wafer or a gallium arsenide wafer, with additional layers and structures then formed on the wafer. However, the use of such a semiconductor material substrate as a starting point is not essential, as conventional techniques allow the use of other substrates, such as quartz, with an appropriate semiconductor material grown or otherwise formed on or bonded to such substrate. In all cases, the resulting devices would be “semiconductor devices,” as discussed herein.
Using the example of semiconductor die which include photo-voltaic cells, commonly referred to as “solar cells,” many if not most applications of solar cells require the use of multiple such cells in order to form a useful assembly, such as a solar panel. Such solar panels may range from relatively small, such as only a few square inches, as might be used to provide power to a portable, consumer-type device, to very large solar panels, several square feet in size, as might be used, for example, either alone or with a number of comparable panels, such as in a rooftop installation on a building.
Additionally, as is well-known in the art, regardless of the ultimate size of the solar panel, individual solar cells are not susceptible to being significantly scaled in size, and thus are typically relatively small structures, often having an area on the order of approximately 1.5 to 8 sq. mm. For example, a conventional, individual solar cell, typically a simple photodiode, can produce somewhere between approximately 0.35 and 0.8V, with some more complex, very high efficiency cells generating up to approximately 2.5V, depending upon the materials and construction used in the cell. However, to produce adequate voltages and currents for most end purposes, multiple solar cells must be used in combination, and each solar cell must be electrically isolated from other solar cells. For example, if there is electrical communication between solar cells, such as electron migration through a common substrate, the diode properties of each solar cell will be compromised, leading to loss of efficiency in the cell, if not failure of the solar cell. Some attempts to achieve this isolation involve doping of the semiconductor substrate to establish diffusion barriers, or neutral zones, within the substrate and between the solar cells. While such steps can be reasonably effective, they also significantly increase the difficulty of processing the wafers, as it can be difficult to establish the isolation regions without impairing the semiconductor properties of the adjacent regions in the substrate. Additionally, such diffusion operations increase the time and complexity, and thus cost, of manufacture of the solar cells.
Because of the difficulties of such processing, the more common strategy is to physically singulate each of the solar cells from the wafer in which they were processed. Each singulated solar cell is then individually removed from the remainder of the diced wafer, and individually placed, such as through use of a placement device known in the industry as “pick and place” equipment, on a supporting substrate. While such processes are generally satisfactory in terms of the performance of the resulting device, the processes are relatively inefficient, requiring individual movement of each individual cell, and the separate alignment of each such cell with the supporting substrate. Since it is not uncommon for even a relatively small solar panel assembly to include tens, if not hundreds of discrete solar cells, the process can be undesirably time-consuming, and therefore costly.
Accordingly, the present invention provides a new method of assembling semiconductor device components, including but not limited to solar cells, to a supporting substrate; with such methods providing efficiencies not present in prior art methods.